From the vibration in the early game handles to the modern portable electronic products, such as, mobile phones or tablet PC, the vibration is generated by the built-in actuators. The early actuators mostly used an eccentric rotating mass (ERM) motor to provide vibration. The vibration function not only provides a reminder when the product is in mute mode, but also as a feedback mechanism in the use of keypad-free operation. The vibration feedback allows the user to feel a slight vibration when using the electronic product equipped with the actuator, prompting the user to complete the interactive operation.
The ERM motor is known to show the drawbacks of slow response, high power consumption, complex structure and easy to damage, and in recent years, with the emergence demand on fast response and low power consumption, the linear resonant actuator (LRA) has replaced the ERM motor to become the mainstream choice to provide the vibration function in portable electronic devices. The main reason is because the LRA uses the Lorentz force generated by electromagnetic effects to drive the movable part in a simple harmonic motion to cause vibration. Compared with the ERM motor, the LRA has the advantages of faster response, lower power consumption, simpler structure and more durable.
The conventional LRA comprises a movable structure, a coil, a elastic suspension system and a housing. The movable structure comprises a magnetic-permeable element, and two magnets. The two magnets are disposed respectively at two opposite sides of the magnetic-permeable element. The coil is fixed to the housing and surrounds the magnetic-permeable element. The elastic suspension system comprises two elastic sheets, with each elastic sheet having a fixed portion, a suspension portion and an engaging portion. The fixed portion of each elastic sheet is fixed to the housing, and the suspension portion is disposed between the fixed portion and the engaging portion. The engaging portion of each elastic sheet is engaged respectively to one side of the magnet away from the magnetic-permeable element. When a continuous alternating current (A/C) current flows through the coil, according to Fleming's left-hand law, the Lorentz force generated by the electromagnetic effect drives the movable structure to move in a first direction with respect to the coil; when the current direction changes, the movable structure moves in a second direction with respect to the coil opposite to the first direction; therefore, a simple harmonic motion (SHM) is generated. The elastic suspension system keeps the movable structure within a fixed range and creates vibration sensation of different frequencies. When the coil is powered off, the elastic suspension system returns the movable structure to the original position.
In general, the vibration effect provided by the LRA to the portable electronic product in parallel movement is superior to that provided in the left and right swing motion. However, the suspension portion of each elastic sheet of the elastic suspension system in the conventional LRA has only one bend and the angle at the bend is equal to or less than 90°, resulting in that the movable structure, in a simple harmonic motion, is actually performing a left-and-right swing with the fixed portions of the two elastic sheets as fulcrums, instead of a parallel movement, which reduces vibration effect and leads to the vibration effect provided to the portable electronic product less than expected.
In order to solve the above problems, a general approach is to directly increase the current to the coil to enhance the vibration effect of the LRA. However, this approach will lead to a significant increase in the temperature and power consumption of the LRA, which leads to the problem of overheating and power consumption for portable electronic products with LRA.